Some manufacturers rely on extremely pure chemicals in the manufacturing process. Many such chemicals are used in liquid form, and may be provided by a chemical manufacturer with a specified level of purity. In some cases, such as semiconductor-grade water, such liquids are generated in a pure form on-site by a semiconductor manufacturer. Of particular concern in the semiconductor context are metal ion contaminants, particularly sodium that can poison semiconductor devices by causing a shift of transistor threshold voltage to the point that a semiconductor device becomes nonfunctional. In high enough concentration, such contaminants may reduce product yield, while in lower concentration the contaminant may reduce long-term reliability of the device.
Manufacturers often determine the level of impurities in the liquid chemicals used. A common protocol is to provide a sample to a service provider who characterizes the species and concentration of impurities and provides a report of the results. A common technique used to characterize the level of impurities in the sample is inductively-coupled plasma mass spectrometry (ICP-MS). While characterization using ICP-MS generally can measure impurity concentrations as low as parts-per-trillion (PPT), in some cases the manufacturer may require even lower levels of contamination.
Furthermore, the service provider is generally not co-located with the manufacturing facility, so the sample may be transported by courier in a container to the provider location. Such transportation inherently risks contamination from the container, the courier, or handling by the provider. Some manufacturers, such as semiconductor manufacturers, operate facilities such as clean rooms, in which contamination is minimized by stringent protocols. In such cases, it may be counterproductive to transport a sample of a liquid outside of the facility to another site for analysis, thereby risking contamination.
What is needed is a method of characterizing contamination of water that overcomes the limitations of currently existing methods.